The present invention relates to a diaphragm switching apparatus for switching a diaphragm by utilizing a driving force of a focus motor used for driving a focus lens.
For switching a diaphragm in a camera or the like, an actuator such as a plunger has conventionally been employed. However, in order to reduce the size, weight, and cost of cameras, other driving sources mounted in a camera, such as a focus motor for driving a focus lens, for example, may be used for switching the diaphragm with a driving force of the focus motor.
Specifically, a diaphragm switching apparatus 100 shown in FIG. 8 maybe considered. This diaphragm switching apparatus 100 comprises a gear 101 adapted to rotate in response to a driving force of a focus motor; a shaft 102 rotatably supporting the gear 101; a diaphragm switching member 103 secured to the axis 102 and adapted to rotate together with the shaft 102; a compression spring 106 for urging the gear 101 away from the diaphragm switching member 103 by way of a washer 105 by receiving a reaction force from the diaphragm switching member 103 by way of a washer 104; and an E ring 108, fitted onto the shaft 102, for receiving the gear 101 urged by the compression spring 106 by way of a washer 107.
The diaphragm switching member 103 comprises a cylindrical barrel 103a in which the shaft 102 is press-fitted, and a lug-shaped protrusion 103b extending from the barrel 103a toward a diaphragm switching lever which is not depicted. The protrusion 103b engages the diaphragm switching lever. The diaphragm switching lever rotates within a predetermined angle range, and switches the diaphragm in two stages of open and stop-down by back-and-force actions of the angular switching.
First, in the diaphragm switching caused by the diaphragm switching apparatus 100, the gear 101 rotates in response to the driving force of the focus motor at the time of focusing. Since the gear 101 is urged by the compression spring 106 so as to be pressed against the E ring 108, the shaft 102 rotates due to a frictional force, and the diaphragm switching member 103 rotates together with the shaft 102. Here, the diaphragm switching member 103 causes the diaphragm switching lever engaged with the protrusion 103b to rotate by a predetermined angle, thereby switching the diaphragm. Then, while the diaphragm switching member 103 and shaft 102 stop rotating at the same time when the diaphragm switching lever stops, the gear 101 rotates in response to the driving force of the focus motor until the driving of the focus lens ends. During this time, the gear 101 idles, thus attaining a slipping rotation state.
In the above-mentioned diaphragm switching apparatus 100, however, not only the gear 101 but also the washers 104, 105, 107 and compression spring 106 are rotatably supported by the shaft 102. Therefore, when the gear 101 attains a slipping rotation state as the diaphragm switching member 103 and shaft 102 stop rotating upon switching the diaphragm, members attaining a slipping rotation state do not become stable. For example, the washers 105, 107 may rotate together with the gear 101, thereby attaining a slipping rotation state, or the compression spring 106 may also rotate together and attain a slipping rotation state. In particular, when the direction of rotation changes, the site of slippage may change, whereby the load imparted on the driving of the focus motor fluctuates in the slipping rotation state. Since the E ring 108 is press-fitted in a groove formed in the shaft 102, it is not always placed at right angles. When the E ring 108 is inserted obliquely, for example, the washer 107 may tilt and thereby fail to receive the gear 101 in a stable state, i.e., at right angles with respect to the shaft 102, whereby the slipping state becomes unstable.
As a consequence, a large fluctuation may occur in the load applied to the focus motor in the slipping rotation state, which may apply a heavy load to the focus motor, whereby the focus motor may cause malfunctions. For preventing the focus motor from malfunctioning, the torque of focus motor must be set while assuming the highest load, which leads the focus motor to enhance its size, power consumption, and the like, thus opposing the tendency of cameras to reduce their size, weight, and cost.
In view of such circumstances, it is an object of the present invention to provide a diaphragm switching apparatus which can stably switch a diaphragm by using a driving force of a focus motor.
Namely, the diaphragm switching apparatus in accordance with one aspect of the present invention comprises a gear adapted to rotate in response to a driving force of a focus motor used for driving a focus lens; a shaft for rotatably supporting the gear; diaphragm switching means, secured to the shaft and adapted to rotate together with the axis, for switching a diaphragm as the shaft rotates; an intermediate member, attached to the shaft so as to be axially slidable, engaging the diaphragm switching means so as to rotate together with the shaft; urging means for urging the gear away from the diaphragm switching means by way of the intermediate member by receiving a reaction force from the diaphragm switching means; and a holding part for receiving the gear urged by the urging means.
According to this aspect of the present invention, the intermediate member engages the diaphragm switching means, whereas the urging means is placed in contact with the diaphragm switching means and the intermediate member. Therefore, when the diaphragm switching means and shaft stop rotating upon switching the diaphragm, the intermediate member and urging means also stop rotating, thus leaving only the gear to be maintained in a rotating state with respect to the intermediate member and the brim in response to the driving force of the focus motor until the driving of the focus motor ends. Therefore, fluctuations in the load applied to the focus motor in the slipping rotation state can be reduced, whereby the focus lens can be prevented from malfunctioning due to a heavy load applied to the focus motor. Also, since fluctuations in the load applied to the focus motor in the slipping rotation state are small, the torque of focus motor can be set low, whereby the focus motor can reduce its size, weight, and power consumption.
The diaphragm switching apparatus in accordance with another aspect of the present invention is characterized in that the holding part is a brim projecting from the outer periphery of the shaft.
According to this aspect of the present invention, the brim yields neither rattling nor tilting with respect to the shaft, thus being able to receive the gear urged by the urging means in a stable state. As a consequence, fluctuations in the load applied to the focus motor when the gear rotates in a slipping fashion can further be reduced.
The diaphragm switching apparatus in accordance with still another aspect of the present invention is characterized in that a low-friction member is disposed between the intermediate member and the gear and/or between the holding part and the gear.
According to this aspect of the present invention, since a low-friction member is disposed, the frictional force of the gear with respect to the intermediate member and holding part can be reduced when the gear rotates in a slipping fashion, whereby the load applied to the focus motor can be lowered. Therefore, the torque of focus motor can be set lower, whereby the focus motor can further reduce its size, weight, and power consumption.
The diaphragm switching apparatus in accordance with still another aspect of the present invention is characterized in that the urging means is an elastic member such as a compression spring or rubber material, and that the urging force of the urging means is made adjustable by changing the distance between the diaphragm switching means and the holding part.
According to this aspect of the present invention, the distance between the diaphragm switching means and the holding part is changed, so as to adjust the urging force of the urging means, whereby the torque of gear can be adjusted minutely.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.